The present invention relates to a communication system that uses a shared control channel to transmit individual control information to a plurality of respective user terminals, a base station device, a user terminal, an individual control information transmission reception method and individual control information transmission method thereof.
In a mobile communication system that performs packet communication, a base station device performs scheduling based on the reception environment of each user terminal (User Equipment; UE), and assigns radio communication resources to each respective user terminal (UE). Normally, information for assigning resources is transmitted to each respective UE from a base station via a shared control channel, and each UE receives that resource assignment information from that shared control channel and detects whether or not there is assignment information intended for itself. When a downlink resource is assigned to a UE, the UE extracts the data that is intended for itself from the assigned resource in the down-direction and demodulates that data. Moreover, when an uplink resource is assigned to a UE, the UE uses the assigned resource to transmit data that is stored in a transmission buffer to the base station.
In 3GPP HSDPA (High Speed Downlink Packet Access) specifications, a base station uses a HS-PDSCH (High-Speed Physical Downlink Shared Channel) to perform downlink packet transmission, and uses a HS-SCCH (High-Speed Shared Control Channel) to transmit resource assignment information to each respective UE. In other words, in HSDPA, the HS-SCCH and HS-PDSCH are both shared channels in the down direction, and the HS-SCCH transmits various parameters related to data that is to be transmitted over the HS-PDSCH. These parameters can be, for example, information such as destination information that indicates which UE data is to be transmitted to, a code number, transmission format information and the like. The transmission format includes information such as bit-rate information, modulation method information, encoding rate information, and the like.
In 3GPP LTE (Long Term Evolution) specifications, the base station employs OFDMA (Orthogonal Frequency Division Multiplex Access) as the downlink transmission method. As shown in FIG. 16, in this LTE, a shared control channel is placed in the starting section of a subframe 1, and resource assignment information is transmitted to each UE. Subframe 1 is comprised of symbols for the number of subcarriers×0.5 msec, with a shared control channel 2 located at the start, a data channel 3 is located after the shared control channel 2, with data for a plurality of UE (User#a, User#b, User#c, . . . ) being frequency multiplexed and time multiplexed in the data channel 3. In subframe 1, C is a control signal, D is a transmission data signal and R is a pilot signal (reference signal). The pilot signals R are discretely arranged in the frequency direction and time direction, and a UE uses the pilot signal to estimate a channel, and by performing an averaging process and interpolation process in the frequency direction and time direction, a UE estimates a channel for each subcarrier.
A user identifier (UE-ID) is added to the resource assignment information for each UE that is transmitted via the shared control channel 2 such that a UE can select its own resource assignment information by referencing the UE-ID. The resource assignment information may include information identifying an uplink or downlink frequency band, transmission formation information, MIMO transmission information, and the like. In the case where the transmission order of the resource assignment information for each UE in the shared control channel is already known, a UE can detect and extract resource assignment information that is assigned for itself according to that order without having to add a UE-ID, and can then perform the specified transmission or reception control. However, in HSDPA or LTE, the transmission order for each UE in the shared control channel of the resource assignment information is not known. Therefore, each UE references the UE-ID that is added to the resource assignment information to identify and select its own resource assignment information.
Incidentally, in a shared control channel in 3GPP LTE, TPC commands for transmission power control (TPC), TA commands for transmission timing adjustment and ACK/NACK, which indicates whether or not uplink (UP) data is successfully received, are scheduled to be transmitted in addition to the resource assignment information. TPC is a technique of comparing target reception power with the actual reception power and adjusting the transmission power of the UE so that both match, and is effective in increasing the system capacity by suppressing interference between UP signals from different UE. The TA is an essential function for a system such as 3GPP LTE that requires uplink synchronization, and is a technique of adjusting the transmission timing of a UE so that actual reception timing coincides with the ideal reception timing. Generally, as a UE moves, the reception power or the reception timing at the base station deviated from the target value, so the base station measures the amount that the reception power or reception timing differs from the target value, then, in order to make that difference zero, sends a TPC command or TA command to the UE and controls the transmission power or transmission timing of the UE. In first related art, these TPC commands and TA commands are collectively transmitted to each UE together with the resource assignment information (refer to 3GPP TSG RAN WG1 Meeting #47, Riga, Latvia, R1-063070).
ACK/NACK is feedback information that expresses a confirmation of whether or not data has arrived correctly using the resource assigned by the shared control channel. Second related art proposes suppressing an increase in the number of control bits by correlating the position of the resource assignment information in the shared control channel and the position of the ACK/NACK for the UP data transmission that uses that assigned resource (refer to 3GPP TSG RAN WG1 Meeting #47bis, Sorrento, Italy, R1-070105). Presuming that a UE-ID has been added to the ACK/NACK, a few UE-ID identification bits are necessary for transmitting one ACK/NACK bit. Therefore, this second related art is a technique of storing the order in the shared control channel of resource assignment information for each UE, for example UE#01→UE#05→UE#04→UE#08→ . . . , and transmitting ACK/NACK information to each UE in the same order as this resource assignment information. In other words, in this second related art, the base station: (1) at timing TA, stores the transmission order on the shared control channel of the UP resource assignment information for each UE; (2) at timing TB, checks for each UE whether or not data was properly received using the assigned resource; and (3) at timing TC, places confirmation information (ACK/NACK) for each UE that indicates the reception result on the shared control channel according to the aforementioned transmission order and notifies the UE. After a UE knows the transmission order of its own UP resource assignment information, the UE obtains the confirmation information (ACK/NACK) in that order and performs retransmission control.
The second related art uses the characteristic that, when the timing for transmitting the resource assignment information is different from the timing for transmitting the confirmation ACK/NACK, transmission of the UP resource assignment information and the ACK/NACK information for the UP transmission data must be performed one-to-one. With this second related art, the transmission order of the resource assignment information is used, however, it is not necessary to arrange the resource assignment information in accordance with a certain rule. In addition, in this second related art, there is no need to add a UE-ID to the ACK/NACK information, so this second related art has the merit of being capable of reducing the number of bits used.